Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is, therefore, classified structurally as a framework silicate mineral and compositionally as an oxide mineral. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.
Spinel is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl
2O
4 in the cubic crystal system. Its name comes from the Latin word spinella, a diminutive form of spine, in reference to its pointed crystals.
The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. The name chrysoberyl is derived from the Greek words χρυσός chrysos and βήρυλλος beryllos, meaning "a gold-white spar". Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones, although they both contain beryllium. Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the Mohs scale of mineral hardness, between corundum (9) and topaz (8).
René Just Haüy FRS MWS FRSE was a French priest and mineralogist, commonly styled the Abbé Haüy after he was made an honorary canon of Notre Dame. Due to his innovative work on crystal structure and his four-volume Traité de Minéralogie (1801), he is often referred to as the "Father of Modern Crystallography". During the French Revolution he also helped to establish the metric system.
Willemite is a zinc silicate mineral and a minor ore of zinc. It is highly fluorescent (green) under shortwave ultraviolet light. It occurs in a variety of colors in daylight, in fibrous masses and apple-green gemmy masses. Troostite is a variant in which part of the zinc is partly replaced by manganese, it occurs in solid brown masses.
Crystal twinning occurs when two or more adjacent crystals of the same mineral are oriented so that they share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals that are tightly bonded to each other. The surface along which the lattice points are shared in twinned crystals is called a composition surface or twin plane.
Alphonse Francois Renard, Belgian geologist and petrographer, was born at Ronse, in East Flanders, on 27 September 1842. He was educated for the church of Rome, and from 1866 to 1869 he was superintendent at the college de la Paix, Namur.
Georges Friedel was a French mineralogist and crystallographer.
Friedel's law, named after Georges Friedel, is a property of Fourier transforms of real functions.
The Gallery of Mineralogy and Geology is a part of the French National Museum of Natural History. It is situated in the Jardin des plantes in Paris near the gare d'Austerlitz train station. The gallery displays a collection of crystals, gemstones and minerals parmi les plus anciennes et les plus prestigieuses du monde.
Friedel's salt is an anion exchanger mineral belonging to the family of the layered double hydroxides (LDHs). It has affinity for anions as chloride and iodide and is capable of retaining them to a certain extent in its crystallographical structure.
The Wulff construction is a method to determine the equilibrium shape of a droplet or crystal of fixed volume inside a separate phase. Energy minimization arguments are used to show that certain crystal planes are preferred over others, giving the crystal its shape. It is of fundamental importance in a number of areas ranging from the shape of nanoparticles and precipitates to nucleation. It also has more applied relevance in areas such as the shapes of active particles in heterogeneous catalysis.
Acicular, in mineralogy, refers to a crystal habit composed of slender, needle-like crystals. Crystals with this habit tend to be fragile. Complete, undamaged acicular specimens are uncommon.
An icosahedral twin is a nanostructure found in atomic clusters and also nanoparticles with some thousands of atoms. These clusters are twenty-faced, with twenty interlinked tetrahedral crystals joined along triangular faces having three-fold symmetry. A related, more common structure has five units similarly arranged with twinning, which were known as "fivelings" in the 19th century, more recently as "decahedral multiply twinned particles", "pentagonal particles" or "star particles". A variety of different methods lead to the icosahedral form at size scales where surface energies are more important than those from the bulk.
Maurice Kleman was a French physicist involved in experimental and theoretical studies of the physics of defects; he has covered various fields of research, from condensed matter to heliophysics. As an author, he has been collected by libraries worldwide.
Georges Deicha was a French geologist and mineralogist, known for his pioneering work on fluid inclusions.
Rubellite is the red or pink variety of tourmaline and is a member of elbaite. Rubellite is also the rarest gem in its family. It is occasionally mistaken for ruby. These gems typically contain inclusions.
Gabriel Delafosse was a French mineralogist who worked at the Natural History Museum in Paris and for sometime at the University of Paris. He contributed to development of the idea of unit cells in crystallography. The mineral Delafossite is named after him. He was one of the founding members of the Société Geologique de France.
Henri Léon Ungemach was an Alsatian mineralogist who made a collection of minerals, nearly 3000 of which are now held at the Muséum National d’Histoire Naturelle in Paris. He described minerals using their crystal geometry. The minerals Ungemachite and Clino-Ungemachite are named after him. He also collected insects, molluscs and plants during his travels.
The law of constancy of interfacial angles is an empirical law in the fields of crystallography and mineralogy concerning the shape, or morphology, of crystals. The law states that the angles between adjacent corresponding faces of crystals of a particular substance are always constant despite the different shapes, sizes, and mode of growth of crystals. The law is also named the first law of crystallography or Steno's law.
